Recently, semiconductor devices have become highly-integrated and are being operated at high speed. Accordingly, the size of the transistors in semiconductor devices has become gradually reduced. As the integration degree of the transistors increases, a metal line of the semiconductor device is fabricated in a micro size. As a result, signals applied to the metal line may become delayed or distorted and thus the high-speed operation of the semiconductor device is interrupted.
In order to solve such a problem, a metal line using copper has been rapidly developed. The copper line is used because the copper line has lower resistance and higher electro-migration resistance characteristics as compared with those of aluminum or an aluminum alloy widely used as the metal line material of semiconductor devices.
In order to form a copper line, a copper layer is formed and then must be etched. However, different from aluminum, copper is not easily etched and the surface of a copper layer is rapidly oxidized in an atmosphere. Accordingly, a damascene process has been developed in order to solve such a problem when forming a copper line.
However, in such a damascene process, a contact hole having a micro-size is sensitive even to a small factor, and is easily damaged. In addition, the photoresist (NOVOLAC) typically used for filling the contact hole may cause defects to the contact hole.
Thus, there exists a need in the art for an improved method of fabricating a semiconductor device.